ABSTRACT Intensification of the eutrophication process in surface water leads to an increase in the intensity and frequency of cyanobacterial blooms, compromising the availability of drinking water. Therefore, the aim of this study was to investigate the spatio-temporal dynamics of cyanobacteria and identify the most important nutrients for such dynamics in a semiarid artificial lake, the Orós reservoir, in north-eastern Brazil. Seventy-seven water samples were collected in 11 campaigns (six during the dry season and five during the rainy season) from seven points. The attributes under investigation were the Secchi transparency, turbidity, pH, apparent colour, electrical conductivity, total solids, total phosphorus, soluble orthophosphate content, total Kjeldahl nitrogen, ammonia content, nitrate content, and cyanobacteria dynamics, resulting in a total of 924 samples (number of campaigns × number of points × number of attributes). Principal component analysis and cluster analysis were used to investigate the significance and determinant attributes of the spatio-temporal dynamics of cyanobacteria. Of the 17 species of cyanobacteria identified, 10 accounted for 72.47% of the total accumulated variance. During the rainy season, four homogeneous groups of cyanobacteria formed, whereas during the dry season, only three groups formed. The greatest concentrations occurred during the dry season, notably for Aphanocapsa spp., Cylindrospermopsis sp., and Geitlerinema sp., which are potentially toxic and show a greater affinity to the physical attributes of water. Climate seasonality was decisive in the spatio-temporal dynamics of cyanobacteria, and high transparency values limited excessive proliferation of the dominant species.

ABSTRACT In semiarid regions with greater climatic variability, including prolonged droughts and delayed rainy seasons, supplemental irrigation is critical to ensuring yields of forage cactus pear. The objective was to evaluate root distribution and nutrient concentration and accumulation in ‘Gigante’ forage cactus pear subjected to different irrigation regimes. Seven irrigation regimes were tested: no irrigation (rainfed); five liters of medium-salinity water, with an electrical conductivity (EC) of 0.75 dS m−1, applied per linear meter every 15 days; 7% reference evapotranspiration (ETo) with a 15-d irrigation interval (II); 15% ETo with a 7-d II; 33% ETo with a 3-d II; 50% ETo with a 2-d II; and 100% ETo, irrigated daily - high-salinity water, EC of 3.6 dS m−1, was used in the last five treatments. The treatments were laid out in a randomized block design with four replicates. Roots developed best in plants irrigated at 50% ETo with a 7-d II. Applying high-salinity water at 15% ETo with a 7-d irrigation interval promotes higher concentrations of P, Ca, Mg and S in cladodes of cactus pear. Applying high-salinity water at 33% ETo with a 3-d II promotes higher uptake/accumulation of P, Ca, Mg, S and Zn in cladodes of ‘Gigante’ forage cactus pear.

ABSTRACT Arrowroot (Maranta arundinaceae), a traditional plant used to extract medicinal starch that is gluten-free and of excellent nutritional quality, is understudied for its growth and development in the organic crop system. The objective of this study was to evaluate the growth and photoassimilate partitioning in plants of two cultivars, Comum and Seta arrowroot. The design was performed in random blocks with four repetitions. At 57 days after planting (DAP), the plants were collected at regular intervals of 25 days throughout the crop cycle, and the dry mass was determined. Growth analysis was performed using the primary data. The cultivars Comum and Seta show maximum absolute growth rates of 10.51 and 12.42 g plant−1 day−1 and the maximum leaf area index (LAI) of 18.74 and 14.62, as recorded for 216 and 205 DAP, respectively. The higher absolute growth rate and higher growth of arrowroot plants in a shorter time indicate greater precocity of cultivar Seta compared to Comum. The photoassimilate partitioning is balanced between the aerial parts and rhizomes at the end of the cycle. Both cultivars can be recommended for the organic crop system in the Zona da Mata region of Minas Gerais.

ABSTRACT Macrophomina (Botryosphaeriaceae) is one of the main genera of soilborne phytopathogenic fungi, which causes root and seed rot in more than 800 host plants worldwide. Recent phylogenetic studies identified the species M. phaseolina and M. pseudophaseolina in Trianthema portulacastrum and Boerhavia diffusa in melon and watermelon production areas in northeastern Brazil. Therefore, the objective of this study was: i) to verify the effect of temperature and salinity on the mycelial growth of M. phaseolina, M. pseudophaseolina and M. euphorbiicola, ii) to assess their pathogenicity on melon and watermelon seedlings, and iii) to determine their sensitivity to the fungicide carbendazim. The optimal temperature for mycelial growth rate (MGR) for Macrophomina spp. ranged from 27.18 ºC (CMM4771 – M. pseudophaseolina) to 31.80 ºC (CMM4763 – M. phaseolina). For the effect of salinity on mycelial growth of Macrophomina isolates, the EC50 ranged from 103.76 (CMM4868 – M. euphorbiicola) to 315.25 mM (CMM4801 – M. pseudophaseolina). The pathogenicity test demonstrated that M. phaseolina, M. pseudophaseolina and M. euphorbiicola are pathogenic on melon with M. phaseolina exhibiting a higher level of virulence. Macrophomina euphorbiicola isolates did not cause disease in watermelon. The most sensitive isolates to the fungicide carbendazim were CMM4868, CMM4867 (M. euphorbiicola) and CMM1531 (M. phaseolina) with EC50 of 0.003, 0.012 and 0.012 mg.L-1 a.i., respectively. All Macrophomina spp. used in these experiments were pathogenic to the tested melon and watermelon cultivars with the exception of the M. euphorbiicola isolate that did not cause damage to watermelon.

ABSTRACT Understanding the behaviour of herbicides in the soil can contribute to adapting the correct dose for efficient weed control with less environmental impact. In this study, we sought to evaluate the factors involved in the sorption, desorption, half-life and leaching processes of sulfometuron-methyl in three soil classes: Cambissolo Háplico (CX) (Inceptisol), Latossolo Vermelho (LV) (Oxisol) and Neossolo Quartzarênico (RQ) (Entisol). The sorption and desorption tests were performed using the “batch equilibrium" method. The studies of degradation and formation of metabolites were estimated from the half-life at the end of 180 days. Leaching potential was estimated by testing PVC columns filled with soil. Analyses were performed by ultra-performance liquid chromatography coupled to a mass spectrometer for herbicide quantification. The higher sorption of sulfometuron-methyl in LV (2.81) is related to the low pH (4.7) and mineralogical composition, mainly due to the higher concentration of Fe and Al oxides in this soil, influencing the lower desorption of the herbicide in LV (0.59). This result contributed to more remarkable herbicide persistence in this soil, reducing the molecules available in the solution for degradation. These results contributed to the longer half-life (19 days) in LV compared to the other soils. Among the studied soils, RQ had the highest risk of transport of sulfometuron-methyl based on the GUS Index (2.2) due to its greater desorption (0.34). The results showed that the studied processes are dependent on the physical, chemical and mineralogical attributes of the different classes of soils.

ABSTRACT Soybeans are among the world’s main crops because they are excellent sources of proteins, micronutrients, and oil. Considering that abiotic stress affects agribusiness, resulting in losses, the grain yield of the crop must be maintained even at high temperatures. In this context, the objective of this study was to select markers related to soybean yield assessed under high temperatures, using associative mapping. The mapping population included 80 soybean PIs and 15 controls. For phenotyping, genotypes were evaluated at high temperatures in an experiment conducted in Teresina (in the state of Piauí) and four characters of interest for agronomy were evaluated: height of the plant when mature, agronomic value, 100-seed weight, and grain yield. Genotyping was carried out using the Affymetrix Platform (180 K Axiom® Soybean Genotyping Array), and the imbalance in the connection between pairs of markers was calculated through the coefficient of determination using the fast permutation test. The analysis of the association between markers and the phenotype of interest was carried out using a generalized linear model approach, including phenotyping data, SNP markers, and information on population structure. The results revealed that 34.06% of loci showed a significant linkage disequilibrium (p < 0.001), and 16 significant associations were found for the four characters related to heat tolerance. These associations can aid breeders that aim to incorporate high temperature tolerance in programs of soybean genetic improvement via selection assisted by markers.

ABSTRACT Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. passiflorae (Fop) is the main fungal disease in passion fruit crops. Chlamydospores, which are structures of resistance produced by Fop, allow the fungus survival in the soil for several years and have saprophytic activity. Biofumigation with incorporation of cabbage and bitter cassava has been a viable alternative, among management methods, for the control of soil pathogens. The objective of this work was to evaluate the effect of different plant debris (plant residues) on survival of Fop under laboratory conditions. In vitro tests were carried out with incorporation of leaves of yellow passion fruit, cabbage, bitter cassava, and sweet cassava plants into substrates infested with different Fop isolates. Mycelial growth and chlamydospore production and germination were evaluated. The incorporation of cabbage and bitter cassava debris had a fungistatic effect on Fop, with decreases in mycelial growth and chlamydospore production. The incorporation of cabbage into the substrate totally inhibited the chlamydospore germination in 78% of the evaluated isolates and decreased the germination percentage in the others.

ABSTRACT An experiment was carried out aiming to evaluate the effect of phosphorus rates on beet, in an Oxisol with high phosphorus (P) content, in Jaboticabal city, São Paulo, Brazil. The treatments were arranged in a factorial scheme, in a randomized block experimental design with four replicates. The factors evaluated were P rates (0, 120, 240, 360 and 480 kg ha-1 P2O5) and cultivar ('Early Wonder' and 'Kestrel'). At 50 days after transplanting the seedlings, foliar nitrogen (N), P, potassium (K) and boron (B) contents were evaluated, and there was no effect of the interaction between factors on foliar nutrient contents. The accumulation of these four nutrients was evaluated at harvest. All evaluated nutrients accumulated to higher levels in ‘Early Wonder’ than in 'Kestrel' both in the shoots and tuberous root. N, P and B accumulated more in the tuberous root whilst K accumulated more in the shoots. P dose did not influence the yield. Therefore, phosphate fertilization is not recommended for beet crop when cultivated in an Oxisol with a high content (88 mg dm-3) of available P.

ABSTRACT Pochonia chlamydosporia (Pc) is a nematophagous fungus with saprotrophic activity. However, little is known about the interaction between Pc and green manure. This study aimed to investigate the interaction effects of different green manures and Pc on the control of Meloidogyne javanica in soybean. Two greenhouse experiments were conducted in different periods using a 6 × 2 factorial design, with six replicates. The first factor was green manure application (oat, brachiaria, crotalaria, millet, buckwheat, and untreated control) and the second factor was treatment with Pc (in-furrow application and untreated control). Cover crops were grown separately and applied to pots as green manure 15 days before soybean sowing. At 5 days after sowing, soybean was inoculated with 2 000 eggs and juveniles of M. javanica. At 60 days after inoculation, nematode and vegetative variables were determined. All green manures reduced nematode population levels, especially oat, crotalaria, and buckwheat. Pc treatment did not influence nematode population levels. Soybean plants treated with oat or crotalaria green manure had greater height than untreated plants in both experiments. The effects of factors on shoot fresh and dry weights differed between experiments, and green manure application did not affect root development. The findings confirmed the potential of plant residues to control M. javanica.

ABSTRACT Chalcididae is a family of parasitoids with wide distribution and great richness, with almost 1,500 described species. Its diversity might be greater than that known today, mainly due to the few existing studies and its taxonomic complexity. Studies in semiarid regions are scarce and necessary to contribute to the biogeographic knowledge of the neotropical fauna. Therefore, the objective of this work was to record Chalcididae species that occur in the municipality of Barra do Choça, in the Semiarid region of the state of Bahia, Brazil. Five Malaise traps were distributed in two areas with native vegetation and an area with eucalyptus plantation, which were monitored monthly for two consecutive years. The insects were sorted and specimens of the family Chalcididae were identified at the species level, when possible. A total of 182 specimens from five genera (Aspirrhina Kyrbi, 1883; Brachymeria Westwood, 1829; Conura Spinola, 1837; Dirhinus Dalman, 1818, and Haltichella Spinola, 1811), and 18 species were identified and 32 were morphotyped. The genus Conura was the most abundant and the most diverse, with 12 species identified and 30 potential new species. The native vegetation presented higher abundance and higher taxonomic wealth, mainly in the area at initial stage of succession (capoeira). The eucalyptus area presented low diversity, with predominance of Brachymeria species. The species C. nigricornis presented the highest relative frequency. This study constitutes the first list of Chalcididae species in the Semiarid region of Brazil. The sampling carried out in the state Bahia showed an important diversity of Chalcididae species when compared to other regions of Brazil.